Traditional utility power grids include a centralized power source (such as a coal-powered generator, a nuclear-power generator, a hydroelectric dam generator, wind farm, or others) and centralized management. The “grid” may connect to other power sources as well so that power can be shared across grid infrastructure from different power sources at a macro-level. However, traditionally, the grid includes a substantial amount of infrastructure, such as utility power lines with associated poles and towers, as well as substations to distribute the power. The grid is traditionally based on a massive generator that can provide enough power to satisfy peak demand of interconnected consumers. A consumer can include a dwelling place, a business, a cellphone tower or other utility box, or other user of power. The different consumers can have different peak demands, from the smallest user of energy to large businesses that have high power demands for heavy commercial equipment.
Traditional grid infrastructure is expensive to build and maintain. Furthermore, it requires the pushing of energy out from the central power source to the consumers, which can be hundreds of miles away. The substations and other infrastructure such as neighborhood transformers are controlled by the centralized management to keep voltages in-phase with current delivered on the grid, and keep voltage levels at regulated levels. Typically, motorized equipment drawing power from the grid will cause a degradation of power factor of the grid. On a macro scale, the grid management has attempted to control the power factor disturbance of the grid due to such motorized equipment. Newer switching power supply designs in modern electronics further complicate the power factor and voltage regulation of the grid by requiring reactive power and introducing noise back onto the grid.
Power delivered by the grid generally consists of a real power component and a reactive power component. Real power is power delivered where the voltage waveform and current waveform are perfectly aligned in-phase. Reactive power is power delivered where the voltage waveform and current waveform are not phase-aligned. Reactive power can be leading or lagging, based on the phase difference between the current and voltage waveforms.
Power as seen by a consumer can be understood differently from energy itself provided to calculate the power. Power is typically represented by W dot h or Watt-hours. Multiplying the Watt-hours by the rate charged by the utility provides the dollar amount owed by the consumer to the utility. But energy can be represented in different ways, and can be measured in multiple different ways. Examples include (VA) V dot I (voltage vector multiplied by current vector for volt-amps), V dot I dot PF (voltage vector multiplied by current vector times the power factor for Watts), and the square root of W{circumflex over ( )}2 (square root of Watts squared for volt-amps-reactive). The consumer typically sees the power in Watt-hours which gives the cost of the energy delivered to the premises. Utilities have also started to measure and charge for reactive power consumption at the user premises.
There has been a significant increase in grid consumers adding renewable sources locally at the consumer locale to produce power. The renewable energy sources tend to be solar power and/or wind power, with a very significant number of solar systems being added. One limitation to customer power sources is that they tend to produce power at the same time, and may produce more power than can be used on the grid. The grid infrastructure is traditionally a one-way system, and the real power pushed back from the customer premises toward the central management and the central power source can create issues of grid voltage control and reactive power instability on the grid. These issues have caused grid operators to limit the amount of renewable energy that can be connected to the grid. In some cases, additional hardware or grid infrastructure is required at or near the consumer to control the flow of power back onto the grid.
In addition to the issues caused by renewable sources, the increase in use of air conditioning units and other loads that draw heavily on reactive power create additional strain for the grid management to keep voltage levels at needed levels. Recent heat waves have resulted in rolling brownouts and blackouts. Other times there are temporary interruptions on the grid as equipment interfaces are reset to deal with the changes in load when people return home from work and increase power consumption there. Traditionally, the central management must maintain compliance of grid regulations (such as voltage levels). Whenever something connected to the grid enters an overvoltage scenario, it shuts off from the grid, which can then create additional load on surrounding areas, resulting in larger areas of the grid coming down before the central management can restore grid stability.
Descriptions of certain details and implementations follow, including a description of the figures, which may depict some or all of the embodiments described below, as well as discussing other potential embodiments or implementations of the inventive concepts presented herein.